The present invention is a method and device for engine braking an internal combustion engine. Specifically, the present invention provides method and apparatus for controlling a throttling device located in the engine""s exhaust flow.
The engine of a vehicle is often used as an auxiliary brake to retard vehicle speed. This particularly applies to heavy vehicles, such as trucks and buses. With regard to heavy vehicles of this category, developments over recent years have resulted in engines of much greater power with unchanged cylinder volume. As a result, the average speed at which such vehicles are driven uphill has increased considerably, meaning that the availability of greater braking power when driving downhill is desirable. Normally, some form of throttle valve is incorporated in the exhaust system with the intention of achieving improved engine braking power. This power, however, is relatively low and often less than half the driving power of the engine.
Furthermore, the resistance of such heavy vehicles to driving has decreased over recent years, meaning that the wheel brakes of the vehicles are subjected to greater loads. When driving in hilly terrain, the wheel brakes should be used as little as possible, primarily for safety reasons. The average speed of the vehicle in hilly terrain is therefore greatly influenced by the available engine braking power, which increases the requirement for a more effective engine brake that will also be capable of reducing wear and tear on the wheel brakes and thereby improve running economy.
A variety of suggestions have, therefore, been made regarding methods and apparatuses for increasing the engine braking power of four stroke internal combustion engines.
In EP-A-193142 there is described a method and an apparatus, where a separate valve is used to establish connection between the combustion chamber and the exhaust system. During engine braking operation this valve is constantly open.
According to GB-A2162580 engine braking power is increased by a mechanism which prevents the exhaust valve from closing completely during engine braking operation. This means that the exhaust valve is constantly open during engine braking operation. A similar apparatus is shown in EP-A-269605.
CH-A-118905 describes an engine with a moveable camshaft.
During engine braking operation the inlet valve is constantly closed, while the exhaust valve is opened shortly before the piston reaches its top-dead-center position, and this cycle is repeated for each revolution of the crank shaft. Thus, during engine braking operation this engine works in a sort of two stroke mode.
In U.S. Pat. No. 5,146,890 to Gobert et al, a method of braking is disclosed which requires one to restrict the exhaust flow when entering the braking mode ideally, this is performed with a variable geometry turbocharger; however, by measuring the restriction turbocharger burnout can occur.
A method for engine braking with a four-stroke internal combustion engine includes each engine cylinder (2) having at least one inlet valve (7) and at least one exhaust valve (9) for controlling communication between a combustion chamber (5) in the cylinder (2) and an inlet system (8) and an exhaust system (10) respectively. The communication is characterized by opening the communication between the combustion chamber (5) and the exhaust system (10) when the piston (3) is located in the proximity of its bottom-dead-center position subsequent to the inlet stroke, by closing the communication when the piston (3) has performed less than half the compression stroke and holding the communication closed during part of the compression stroke, by opening the communication when the piston (3) has performed more than half the compression stroke, and by holding the communication open during the remaining part of the compression stoke and during at least a part of the expansion stroke. The communication of the combustion chamber (5) with the exhaust system (10) being effected upstream of a throttling device (13) mounted in the exhaust system and for engine braking being actuated to at least maintain the flow through the exhaust system (10) and therewith not cause an increase in pressure upstream of the throttling device (13).
In another embodiment of the present invention, an arrangement for engine braking with a four-stroke internal combustion engine comprises each cylinder (2) having at least one inlet valve (7) and at least one exhaust valve (9) for controlling communication between the combustion chamber (5) of the cylinder and an inlet system (8) and an exhaust system (10) respectively. The communication is characterized in that the arrangement includes means for opening, during an engine braking operation, a communication between the combustion chamber (5) and the exhaust system (10) when the piston (3) is located in the proximity of its bottom-dead-center position subsequent to the inlet stroke and for closing said communication when the piston (3) has performed less than half the compression stroke; in that means are provided for opening, during an engine braking operation, the communication when the piston (3) has performed more than half the compression stroke and for holding the communication open during the remaining part of the compression stroke and during at least part of the expansion stroke. Further, there is provided in the exhaust system (10) downstream of the connection of the combustion chamber (5) with the exhaust system (10) a throttling device (13) which is operative during an engine braking operation to at least maintain the flow through the exhaust system (10) and therewith not cause an increase in pressure upstream of the throttling device (13).